NOT STARTING?

1972 Oldsmobile 442 • V8 2WD Manual • 45,597 miles

Hey I have a 1972 olds cutlass 442 with a 455 mondello engine she gets fuel from carb, tries to crank over but will not fire, just replaced spark plugs, what could be the problem she has 590hp at the rear wheels and this is driving me nuts, she ran fine out and about then started running rough on the way home we shut her off and now she wont start?